The YM doesn't have native commands for doing that sort of thing, so your Arduino has to send sound modifications to the YM channel playing the sound while the sound is playing.

To add vibrato or pitch bend, your sketch will have to change the fine pitch of the YM channel playing the note in real time, sweeping it plus and minus from the note centre frequency.

To employ the common chiptune trick of using one channel to play a 'chord' by alternating quickly through the three notes of the chord, designate one MIDI channel for that purpose and, when your project receives a note-on 'C' message on that MIDI channel, have your program quickly cycle the YM channel through the three notes of C Major until the corresponding note-off message is received. That kind of thing.

the gfa handbook(gfa programmers reference guide volume1..george miller) has a neat well documented function called "wave"it posses basic application of the 3 channels...the waveforms and noise .....im afraid other than that I cant help ...I deal mainily with midi on the Atari